1. Field of the Invention
The present invention relates to a flexible coupling for transmitting torque between a drive shaft and a driven shaft and for accommodating angular misalignment of the shafts. More particularly, the invention relates to a flexible element manufactured from composite fibers wound and formed into a disc-type or an offset-link configuration.
2. Description of the Prior Art
Flexible couplings for connecting a drive shaft to a driven shaft, which accommodate angular misalignment between the rotating shafts, are well known in the art. Recent advancements in the art endeavor to improve the misalignment-handling capability of couplings, while maintaining the required strength of the coupling. They also attempt to minimize the weight of the coupling. Many advances have been directed toward the flexible elements used in flexible couplings. These elements are pliant enough to accommodate angular misalignment of the shafts, and they are strong enough to transfer the required torque between the shafts, although not all the links always participate in the torque transmission.
For example, consider the known configuration of composite flexible elements pictured in FIGS. 5a-5c. The pins marked with a `D` are attached to the driving flange and those marked with a `d` are attached to the driven flange. When torque is applied to the system shown in FIG. 5a, only three of the six links of the system are subjected to the tensile forces labelled `T`. The links that are subjected to the force `T` are often called driving links. The other three links are commonly referred to as the driven links.
Even though only three links contribute to torque transmission, the flexible element is usually made of six links due to the possibility that the drive shaft may rotate in a clockwise or counterclockwise direction. The six link configuration is also a more practical construction for the case of unitized flexible elements.
As shown in FIG. 5b, the links are arranged in an offset pattern having a total thickness of 2h. Two techniques have been used to achieve such a layout. First, the individual links are separately manufactured and the driving/driven pins are then inserted through the ends of the superposed links. Second, the pins are first inserted on the bolt circle BC diameter shown in FIG. 5a. The lower links `L` are filament wound first and the upper links `U` second.
The links that are used to form the flexible element are of the type shown in FIG. 5c. Due to this filament winding pattern, the links can withstand only tensile forces, not compressive forces. For this reason, the system has been designed, as described above, so that only three of the links are subjected to the tensile forces.
It is interesting to note that the drive/driven shaft are restricted in their diameter due to the amount of space occupied by the conventional flexible member. It is desirable to use as large a shaft as the flexible elements will allow.
Coupling elements fall within two basic categories, the first being offset-link elements. These elements generally comprise a number links connected end-to-end in an offset manner. Each link includes a drive-bushing which receives a pin extending from a flange at one end of a drive-shaft, and a driven-bushing which receives a pin extending from a flange at an opposing end of a driven-shaft. The drive-bushings and driven-bushings are connected to form links, and the links are joined end-to-end in a loop to form the flexible element. The second category includes disc-type flexible elements. These elements generally comprise alternate drive-bushings and driven bushings concentrically arranged within a unitary composite disc.
Prior art flexible coupling elements are limited as to durability, angular misalignment capacity, or both. Originally, both categories of coupling elements comprised thin metal discs or links. The metal was strong enough to withstand the torsional forces, but was not resilient enough to withstand a large angular displacement of the drive shafts. The metal was also relatively heavy, and imposed a considerable load on the drive shaft. As the art progressed, composite elements were developed which enabled the construction of lightweight flexible couplings. These composite elements were also able to withstand a larger misalignment of the shafts. Unfortunately, the torsional strength of the composite elements was less than metal. Current devices attempt to achieve greater angular misalignment capacity and lighter weight without sacrificing the torsional strength and durability of the metal discs. These devices arrange a composite material in a selected high pattern to improve the durability of the coupling. The flexible elements are formed from composite strands repeatedly wound around adjoining drive and driven-bushings. In this connection reference may be had to U.S. Pat. No. 4,377,386. However, in this and other cases the winding pattern results in a flexible element with a small inside diameter. In such an arrangement, a coupling hub inserted through the flexible element must have a smaller bore than with other conventional couplings.